1. Field of the Invention
The present invention relates to a rotator element for an electric motor. More specifically, the present invention relates to a rotator element for an electric mortor having improved fixing structure of permanent magnets.
2. Description of the Related Art
In the Japanese Patent Disclosure 60-109749, a permanent magnet type of rotator element for an electric motor is disclosed. In such type of rotator element, a plurality of permanent magnets are fixed in holes provided at a cylindrical core body of the rotator. The core body is generally made of stacked iron disc-shaped plates. Each of the disc-shaped plates has a plurality of cutouts on the circumference areas. The permanent magnets with opposite pole are alternately inserted into the holes as shown in the Patent Disclosure 60-109749. The core body has a central hole through which a rotator-shaft is inserted. The core body has small holes to fasten the disc-shaped plates together by rivets. Two of the disc-shaped plates located at the outermost sides, which have no cutout portions, are plates for holding the rest of ring-shaped plates together with the rivets.
Due to the difficulties in manufacturing the accurate size of permanent magnets, dimensional tolerance is given to .+-.0.1 mm for instance. Accordingly, some of the permanent magnets cause an insertion problem. The permanent magnet which is in the uppermost limit of the tolerance may fail to be insertable into the hole because the hole is smaller than the magnet. By forcibly inserting such permanent magnet into the hole, it would be broken or deformed. On the other hand, the permanent magnet which is in the lowermost limit of the tolerance causes another problem. In this instance, the permanent magnet is vibrated in the hole during the rotation of the rotator and generates vibration noise. This vibration could cause the permanent magnet to break.